Protists
Key Facts on Protists
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Eukaryotic
Hetereotrophic or autotrophic
Reproduce sexually or asexually
Live in aquatic or other moist environments
Importance of Protists
• Protists play key roles in aquatic ecosystems.
• Protists that perform photosynthesis along
with some other prokaryotes, are the major
producers in the world’s oceans
• Non-photosynthetic protists are consumers
that dominate the lowest levels of most
aquatic food pyramids
Importance of Protists con’t
• Many protists are parasites – they live in, or
on, other organisms
• Most parasites do not harm their host
organism, but some cause serious disease (ex:
malaria, sleeping sickness, ameobic dysentry,
beaver fever)
Beaver Fever
Importance of Protists
• Human Uses of Protists
– sushi (nori is a multicellular protist Porphyra)
– Agar and carrageeenan (both are food additives)
Origin
• Protists were the first eukaryotes – their cells
have a nucleus and organelles bound by
membranes.
• These internal membranes likely developed from
the folded cell membrane of an ancestral
prokaryotic cell.
• This folding would have increased the cell surface
area, allowing the cell to better exchange
materials with its environment. This ability is a
necessary feature of large cells.
Origins
Origins – Chloroplasts & Mitochondria
• Present-day mitochondria and chloroplasts
each have two membranes
• Their inner membranes are similar to those of
their ancestral prokaryote, while their outer
membranes match the cell membranes of the
eukaryotes
Origins – Chloroplasts & Mitochondria
• Present-day mitochondria and chloroplasts
have their own internal chromosomes (DNA)
• These chromosomes are very similar to
prokaryote chromosomes and contain genetic
information used by the organelles
• Mitochondria and chloroplasts reproduce
independently within eukaryotic cells by
binary fission, just as prokaryotes do
Origins – Chloroplasts & Mitochondria
• Because of all of those features, we believe
that mitochondria and chloroplasts are
thought to have originated by endosymbiosis.
– ENDOSYMBIOSIS: a relationship in which a singlecelled organism lives within the cells of another
organism
Origins – Chloroplasts &
Mitochondria....conclusion:
• Mitochondria and chloroplasts were once
prokaryotic organisms. These cells were
engulfed by early anaerobic eukaryotic cells
and incorporated into them.
• We believe that mitochondria were once
aerobic prokaryotes that benefitted from a
rich food supply, while the eukaryotes
benefited from the excess energy released by
the areobic prokaryote
Origins
Typical Protists
• There are no typical protists! Many protists
are parasites that can may or may not harm
their host. Malaria is a disease that is caused
by a harmful protist called Plasmodium that is
transmitted using a mosquito as a vector.
• Protists can be unicellular or multicellular.
They vary in their cell features, ways of
moving, ways of getting nutrients and
methods of reproducing.
• If it is eukaryotic and it’s not a plant, animal or
fungi, it’s a protist!
Ecosystems and Protists
- Protists play key roles in ecosystems as producers or
consumers.
- For example, the large green, red, and brown algae
called seaweeds have gas-filled bladders that help
them float toward the light .
- This allows them to produce energy through
photosynthesis.
- Photosynthetic protists are the primary producers in
aquatic food webs.
- The large kelps, belonging to the brown algae group,
can grow up to a half metre a day and reach a length
of 80 m!
Climate Change and Protists
- Climate change is affecting many protists,
including algae. In aquatic ecosystems the
temperatures of oceans and lakes are rising.
- The water is also becoming more acidic, which
may interfere with some protists’ ability to
produce their outer protective shells.
- Without their protective shells, they may not
survive.
- The loss of these protists may severely damage
food webs that rely on the photosynthetic
products they create.
Life Cycles
• Protists reproduce sexually and asexually
Single Cell Protists
• Asexually – Binary Fission
• Sexually – Conjugation
Multi-cellular Protists
- Sexually – Sex Cells (ie male sperm
and female egg)
Complex Life Cycles – Example Malaria
Malaria
• http://www.youtube.com/watch?v=A2XTlHBf_4
Comprehension Homework:
• 2. Some protists are closely related to animals,
plants or fungi than they are to each other.
What does this suggest about the
classification criteria used for members in this
kingdom.
Homework
• Homework: (Research)
• African sleeping sickness is a serious parasitic disease
caused by the protist, Trypanosoma brucei. Use the
Internet to find out more about this disease. Where in
the world is it most prevalent? How is it spread? What
are the symptoms? Can the disease be effectively
treated?
• Go to the WHO website (or other sites) to learn more
about malaria. How is it spread? How prevalent is it in
the world? How can it be prevented? How is malaria
connected to sickle-cell anemia?
• http://www.youtube.com/watch?v=-zsdYOgTbOk
Videos
• Overview of Protists
• http://www.youtube.com/watch?v=zsdYOgTbOk